Hot gas defrosting system



Oct. 6, 1964 K. QUICK HOT GAS DEFROSTING SYTEM 2 Sheets-Sheet l Filed July 14, 1961 mmbmI Omi) LESTER K QUICK v 'INVEN'TOR- BY y ATTORNEYS.

Oct. 6, 1964 l.. K. QUICK 3,151,470

HOT GAS DEFROSTING SYSTEM Filed July 14, 1361 2 Sheets-Sheet 2 fIOZA IO5A JIS ATTORNEYS.

United States Patent O 3,151,479 HUT GAS DEFRGSTING SYSTEM Lester K. Quicir, 795 W. 8th Ave., Eugene, Greg. Fiied July 14, 1961, Ser. No. 125,040 il Claims. (Cl. 62-273) This invention relates to a refrigeration system and more particularly to such a system adapted to be applied to a commercial installation such as a modern supermarket and is particularly concerned with the defrosting of various refrigerated units that will conventionally be present in such a supermarket.

It is a feature of this invention that lends itself to a defrosting program which may be clock controlled with a single clock controlling the defrosting cycle for all of the refrigeration units.

It is an object of this invention to provide a refrigeration system employing hot gas defrosting so arranged that a superabundant supply of hot gas is available at all times to defrost any one fixture in the store.

It is a further object of this invention to provide a hot gas defrosting system wherein the fluid from a fixture being defrosted with hot gas, which will normally be a mixture of liquid and gas, is passed to a second fixture or slave wherein the refrigerant uid is revaporized after it has served its purpose in defrosting the first unit, thus assuring that no slug of liquid will be returned to the compressor, yet without sacrificing the refrigerating potentiality of the gas which was liquiiied in the process of defrosting the iirst unit.

It is another feature of this invention that in applying hot gas to the fixtures being defrosted the suction lines carrying the gas from the fixtures during the refrigerating cycle are used as hot gas supply in the defrosting cycle.

It is another feature of this invention that due to the fact that the system is clock controlled the same clock may be used to apply electric defrost to the coils and drain pan at the same time that the hot gas is delivered to assure drainage of the melted ice from the fixture concurrent with defrosting.

It is another feature of this invention that it is impossible to overload the compressor motor during defrosting i since at least two fixtures are disconnected from the refrigerant line and only one reconnected and at the end of the defrosting both fixtures involved in the defrosting come back on the line under normal operating conditions, thus presenting no motor overload.

It is another feature of this invention that much less work is required by the refrigeration compressor after defrosting since no appreciable amount of heat is stored in the fixture during defrosting. This has the additional advantage of not increasing the temperature of the fixture due to the defrosting thereof by any objectionable amount and consequently the undesirable consequences of alternately warming up and then cooling down the materials stored in the xture are avoided.

It is another feature of this invention that a much shorter defrosting time is effected to the extent that the defrosting time is really determined by the amount of time it takes to warm up the drain pan and the water drains when using presently conventional drain pan heaters.

It is another feature of this invention that it is econornical, a .i aterial saving being effected by the fact that the only electricity required is to warm the drain pan and that the defrosting time will not normally exceed 20-25% of conventional defrosting time, so that the actual electrical power saving will pay for the installation of the entire defrosting system several times a year.

Particularly with respect to the storage of ice cream, any appreciable rise in the temperature of the frozen `frigerant header 14.

@,iSiA@ Patented Get. 6, i964 cream is sought to be avoided because of a solidifying effect which it has upon the confection. In applying the present invention to fixtures which were not speciiically or ideally designed for the use of this system, it has been found possible to defrost ice cream boxes with a temperature rise of only three degrees, i.e., from -24 F. to -21 F. and it is calculated that this rise can be reduced to 1 F. with ideally designed fixtures.

It is another feature of this invention that the superabundance of hot gas assures positive defrosting not onl of the evaporative coils but also of the return and supply air ducts.

The feature pointed out with respect to ice cream, supra, is also important in the defrosting of self-service meat cases, meat coolers, and the like, as temperature variation is known to be a major factor in the length of time that a frozen product can be preserved.

These and other objects, features, and advantages will Y be apparent from the annexed specification in which:

FIGURE l is a diagrammatical representation of the hot gas defrost system.

FIGURE 2 is a schematic diagram of the clock-controlled circuit for operating various solenoid valves shown in FIGURE l and for energizing the pan heaters as Well as for energizing various fans in the refrigeration tixtures.

Referring now more particularly to FIGURE l, there are in general three modes of operation, the first-mentioned being when both evaporators 21 and 22 function as evaporators independent of each other. The second mode of operation accomplished by electrical switching of various solenoid valves as described later in` connection with FIGURE 2 involves the use of evaporator 21 as an evaporator but with evaporator 22 functioning generally as a condenser for defrosting the same. A third mode of operations involves evaporator 22 functioning as an evaporator and evaporator 21 functioning as a condenser in the process of defrosting the same.

For these purposes the condenser-receiver i0 receives hot compressed gaseous refrigerant from the compressor 31. The various valves indicated by the letter S in FIGURE l are normally closed valves, i.e., they require the application of voltage to open the valves. The various valves shown in FIGURE 1 indicated by the X mark are hand-operated valves which are used only for servicing purposes, i.e., such valves are either manually opened or manually closed, the same being closed when the system requires servicing. In the foregoing description, it is assumed that each of the hand-operated valves are in their fully open positions.

In the first-mentioned mode of operation, i.e., in the so-called refrigeration cycle, the refrigerant passes through valve 11, conduit i2, sight glass 13 to liquid re- From the refrigerant header 14 the refrigerant passes through liquid line solenoid valves 15 and 16 and corresponding liquid lines 1'7 and 18 and through corresponding expansion valves 19 and 20 to evaporators 21 and 22 where the liquid is boiled away to a gas, extracting heat from the fixture in which such evaporators Z1 and 22 are mounted.

WhileFIGURE 1 shows only two evaporators 21 and 22, in practice there may be very many, i.e., more than two, and the system is designed for as many as fifteen or more separated evaporator units. From the evaporators 21 and 22, the refrigerant gas passes through corresponding suction lines 23 and 24, through suction line solenoids 25 and 26, and valves 27 and 28 to suction header 29. From suction header 29 the gaseous refrigerant passes through the main suction line 30 back to the inlet of compressor 31, the outlet of compressor 3l being in communication with the condenser-receiver unit 10, thus completing the refrigerants cycle.

After some use, the evaporators require defrosting, and defrosting is accomplished by selective energization and de-energization of various solenoid valves to accomplish the second and third modes of operation outlined above. Generally, in the defrosting operation one of the evaporator units 21, 22 `functions as an evaporator and the other one of the units 21, 22 operates as a condenser, the units operating in pairs for this purpose.

Thus, supposing it is to be desired to defrost evaporator 22, i.e., to achieve the second mode of operation, solenoid valves 25, 40, and 41 only are energized to open same and solenoid valves 15, 16, 26, 52 and 53 are allowed to close by not energizing same. The result of the foregoing is to pass hot gas from the compressor 31 through conduit 50 and hot gas header 51 through hot gas solenoid d and line 24 to the unit 22 where the hot gas acts to defrost the coils of evaporator unit 22. From the unit 22 the condensed liquid passes through by-pass check valve 42, through conduit 1S, by-pass solenoid valve 41, check valve 41A to conduit 17 and thence through metering expansion valve 19 to the evaporator unit 21 where the liquid formed in the defrosting of evaporator 22 is re-evaporated in evaporator 21 such that no slug of liquid can be returned to the compressor. From the evaporator 21 the completely evaporated gas returns through line 23 and solenoid 25 and hand valve 2'7 to suction line header 29 and then back through the main suction line 30 to the inlet of compressor 31. It should be noted that conduit. 50 from compressor 31 passes hot gas to hot gas header 51 and the hot gas therefrom iiow through the hand valve 40A and solenoid valve 40 to the evaporator unit 22 which at this time functions as a condenser.

When it is desired to defrost the other evaporator 21, i.e., to achieve the third mode of operation, all of the solenoid valves are allowed to close by the conventional means incorporated in the same for biasing the same to closed position and only solenoid valves 26, 52, and 53 are energized to open the same. In such case, substantially the same cycle is followed as in the second mode of operation, but in this case the unit 22 functions as an evaporator and the unit 21 functions as a condenser to accomplish defrosting of fixture 21. Thus, in this third mode of operation hot gas from the compressor 31 passes through conduit 50 and hot gas header 51, through hand valve 52A, hot gas solenoid valve 52 and line 23 to evaporator unit 21 Where the hot gas acts to defrost the evaporator coils. From evaporator unit 21 the condensed liquid passes through by-pass check valve 19A through conduit 17, by-pass solenoid valve 53 and check valve 53A to conduit 18 and thence through metering expansion valve 20 to evaporator 22 where any liquid formed in the defrosting of evaporator 21 is re-evaporated in evaporator 22 so that no slug of liquid can be returned to the compressor. From the evaporator 22 the completely evaporated gas returns through line 24 `and through solenoid valve 26 and hand valve 28 to the suction line header 29 and thence back through main suction line 30 to the inlet of compressor 31.

The electrical circuitry for accomplishing this selective energization of the various solenoid valves in accomplishing the three modes of operation described above is now described in connection with FIGURE 2 wherein the solenoid valves are identified by identical reference numerals. In general, that circuitry in the left in FIGURE 2 pertains to the evaporator unit 21 and like circuitry -to the right in FIGURE 2 pertains to the evaporator unit 22.

These two units are controlled by clocks which are represented in FIGURE 2 by windings 190 and 101, and their corresponding time-controlled switches 100A and 101A, which have opposite terminals thereof connected to a control line bus 102 comprising A.C. lines 102A and 102B, such bus 102 being connected to the source of A.C. voltage 103. lt will be understood that these switches 100A and 101A are time controlled in conventional manner and when closed serve to energize the relay coils and 101 which serve to actuate coresponding single-pole double-throw switches 10d and 105 which are shown in their normal positions, i.e., with the coils 100 and 101 de-energized. The switches 104 and 105 have corresponding movable contacts 1614A, A; stationary run contacts 104B, 105B; and stationary defrost contacts 104C, 105C, the movable contacts 104A and 105A being connected to the A.C. line 102A. The stationary run contacts 104B and`105B are connected to one terminal of corresponding solenoid valves 25 and 26, the other terminal of these valves 25 and 26 each being connected to the other AC. lead 102B. The stationary defrost contact ltiiC is connected to one terminal of each of the following: relay coil 110, heater solenoid 111, solenoid valve 52, and solenoid valve 53, the other terminal of each of these elements being connected to the A.C. line 102B. Likewise, the stationary defrost contact 105C is connected to one terminal of each of the following elements: relay coil 113, heater relay 114, and solenoid valves d0 and 41, the other terminal of each of these elements being connected to the A.C. line 102B.

These relay coils and 113 have associated therewith corresponding normally closed switches 110A, 110B and 113A, 113B. Each of these switches 110A, 110B, 113A, 113B is termed normally closed since they are closed when the corresponding associated winding 110 is cie-energized.

Each fixture in which corresponding evaporator units are disposed is controlled by a temperature-responsive switch 121, 122, switch 121 being in that fixture associated with unit 21 and switch 122 being in that fixture associated with unit 22. Switch 121 is connected in a series circuit which extends from line 102B, through switch 121, solenoid valve 15, normally closed relay switch 110B, normally closed relay switch 113A and line 102A so that valve 15 is controlled in accordance with the temperature in that fixture associated with evaporator 21 (FIGURE l).

Likewise, the temperature-responsive switch 122 is connected in a series circuit which extends from line 102B, through switch 122, through switch 113B, solenoid valve 16, normally closed relay switch 110A and line 102A so that the valve 16 is controlled in accordance with .the temperature in that fixture associated with evaporator 22 (FIGURE 2).

Thus, in the condition illustrated in FIGURE 2 and with the temperature-responsive switches 121 and 122 being closed, the first mode of operation described above is accomplished, i.e., a cooling effect is produced in both evaporators 21 and 22 with the following solenoid valves only being energized and thus being opened for that purpose: valves 15, 25, and 16, 26.

To defrost unit 22, the time-controlled switch 101A is closed to cause movable contact 105A to engage the defrost contact 105C with the result that valve 26 is allowed to close by its biasing means and the valves 40 and 41 are energized and thus opened. Also, it is observed that relay winding 113 is now energized to thereby open its associated switches 113A, 113B. Opening of switch 113A prevents `energization of solenoid 15, i.e., assures closure of valve 1S. Opening of switch 113B prevents energization of solenoid 16, i.e., assures closure of valve 16. Valve 26 remains closed throughout the defrosting of evaporator 22 since the timing of the switches 100A and 101A is such that switches 104 and 105 are not actuated at the same time, i.e., only one defrost contact 104C, 105C being engaged during defrosting operations.

In achieving the third mode of operation, i.e., defrosting of evaporator 21, the time-controlled switch 100A is closed to thereby move the movable contact 104A into engagement with the defrost contact 104C, the switch 105 remaining in its position illustrated in FIGURE 2. This closure of switch 104A, 104C results in energization and thus opening of tbe solenoid valves 52 and 53, the valve 25 being then de-energized and in a closed condition. Also, it is observed that relay winding 110 is now energized to thereby open its associated switches 110A and 110B. Opening of switch 110A prevents energization of solenoid valve 16, i.e., it assures closure of valve 16. Opening of switch 110B prevents energization of valve and assures its closure. Valve 25, however, remains closed since, as mentioned above, the timing of the switches 190A and 101A is such that switches 104 and 105 are not actuated at the same time.

Subsidiary features in FIGURE 2 involve the air fans 130 and 131 associated respestively with evaporator units 21 and 22 and, as shown, the same are energized during each of the three modes of operation described above, i.e., these fans are continuously energized. Also, the previously mentioned relay coils 111 and 114 serve, when energized, i.e., in the defrost condition of corresponding units 21 and 22, to energize conventional-type pan heaters 111A and 114A (FIGURE l). The type of heaters used is considered optional and likewise the fans 130 and 131 may be energized only during portions of the defrost cycle to defrost the air ducts.

While there has been described what is at present considered a preferred embodiment of the present invention, it will be apparent to those skilled in the art that various changes and alterations may be made therein without departing from the essence of the invention, and it is intended to cover herein all such changes and alterations as come within the true spirit and scope of the appended claims.

I claim:

1. In a refrigerating -system having a compressor with a suction side connected to a suction header and a discharge side connected to condenser-receiver means for providing a liquid refrigerant source; a liquid header, connected to the condenser-receiver means, first refrigerating fixture means having first evaporator means having inlet and outlet sides connected between said liquid and suction headers, a plurality of other refrigerating fixtures having other evaporator means having inlet and outlet sides connected between said liquid and suction headers, a hot gas header connected to the discharge side of said cornpressor, first valve means for selectively isolating said first evaporator means from said suction header and connecting one side of said first evaporator means to the hot gas header for receiving hot gaseous refrigerant from said compressor to effect the defrosting of said first evaporator means, at least several of said other evaporator means being connected in the system for normal refrigeration during defrosting of said first evaporator means and returning a superabundant latent heat load to said compressor whereby said hot gaseous refrigerant in said hot gas header has a substantially greater heat load than required for defrosting said first evaporator means, and means for causing a reduced pressure on the inlet side of at least one of said other evaporator means relative to the pressure on the condenser-receiver means and for conducting the refrigerant resulting from defrosting of said first evaporator means from the other side of that first evaporator means into the inlet side of at least one of said other evaporator means downstream4 of the said means for causing reduced pressure, said last-mentioned other evaporator means having a predetermined minimum refrigerant requirement sufficient to vaporize the liquid refrigerant resulting from such defrost. Y

2. The refrigerating system according to claim 1 wherein said heat load of said hot gaseous refrigerant provides the sole heat source for effecting defrost of said first evaporator means. Y

3. In a refrigerating system having a compressor with a suction side connected to a suction header and a discharge side connected to condenser-receiver means for providing a liquid refrigerant source; a liquid header connected to the condenser-receiver means, first refrigerating fixture means having first evaporator means having inlet and youtlet sides connected between said liquid and suction headers, a plurality of other refrigerating fixtures having other evaporator means having inlet and outlet sides connected between said liquid and suction headers, a hot gas header connected to the discharge side of said compressor, first valve means for selectively isolating said first evaporator means from said suction header and connecting one side of said of said first evaporator means to the hot gas header for receiving hot gaseous refrigerant from said compressor to effect the defrosting of said first evaporator means, said other evaporator means being connected in the system for normal refrigeration during defrosting of said first evaporator means and returning a superabundant latent heat load to said compressor whereby said hot gaseous refrigerant in said hot gas header has a substantially greater heat load than required for defrosting said first evaporator means, and means for discontinuing the normal liquid refrigerant supply from the condenser-receiver means to at least one of said other evaporator means during defrosting of said first evaporator means and means for conducting liquid refrigerant resulting from the defrosting of said first evaporator means from the other side of that first evaporator means into the normal liquid refrigerant flow path of the last mentioned said other evaporator means downstream of said means for discontinuing the normal liquid refrigerant supply.

V4. In la refrigerating system having a compressor with a suction side connected to a suction header and a discharge side connected to condenser-receiver means for providing a liquid refrigerant source; a liquid header connected to the condenser-receiver means, first refrigerating fixture means having first evaporator means having inlet and outlet sides connected between said liquid and suction headers, a plurality of other refrigerating fixtures having other evaporator means having inlet and outlet sides connected between said liquid and suction headers, a hot gas header connected to the discharge side of said compressor, first valve means for selectively isolating said first evaporator means from said suction header and connecting one side of said first evaporator means to the hot gas header for receiving hot gaseous refrigerant from said compressor toeffect the defrosting of said first evaporator means, said other evaporator means being connected in the system for normal refrigeration during defrosting of said first evaporator means and retuming a superabundant latent heat load to said compressor whereby said hot gaseous refrigerant in said hot gas header has a substantially greater heat load than required for defrosting said first evaporator means, second valve means for isolating at least one of said other evaporator means from said liquid refrigerant source during defrosting of said first evaporator means, and means for introducing liquid refrigerant resulting from said defrosting of said first evaporator means from the other side of that first evaporator means into the liquid fiow path to said isolated other evaporator means downstream of said second valve means.

5. In a refrigeration system including a compressor having a refrigerant suction side and a high pressure outlet side, condenser-receiver means connected to the high side for condensing hot gaseous refrigerant to a liquid and for maintaining a supply of liquidrefrigerantj the combination of a plurality of refrigerating fixtures each of which has evaporator means for the cooling thereof and for providing -a superabundant heat load on said refrigerant returned to the refrigerant suction side, a liquid line header connected to said condenser-receiver means7 a suction line header connected to the inlet side of said compressor, separate evaporator Vfeed and return lines connecting opposite ends of said evaporator means in parallel refrigerant fiow relation between said liquid line header and said suction line header, a hot gas header connected to the high side of said compressor in parallel flow relation with said condenser-receiver means, hot gas supply lines connected between said hot gas header and each of said evaporator means on the suction line header side thereof, lines connecting the evaporator feed lines of preselected evaporator means to the evaporator feed lines of other evaporator means; valve means in said hot gas supply lines, valve means in said evaporator return lines7 valve means in said evaporator feed lines between said liquid line header and the said lines connecting the feed lines, and valve means in said lines connecting the feed lines; said valve means being selectively positioned for diverting hot gaseous refrigerant from said compressor through said hot gas header to preselected evaporator means for defrosting same whereby said preselected evaporator means functions as an auxiliary condenser means and subsequently diverting said defrost liquid refrigerant through the said line connecting the feed line of that preselected evaporator means to other evaporator means for re-vaporating said defrost liquid refrigerant in the said other evaporator means for returning the refrigerant in gaseous state to said compresser through said suction line header, the said selective positioning of said valve means also discontinuing the normal flow of liquid refrigerant from the condenser-receiver means through said evaporator feed lines to the said preselected evaporator means and said other evaporator `means receiving the said defrost liquid refrigerant.

6. In a refrigerating system employing a plurality of separate refrigerating fixtures each having evaporator coils, a compressor having a suction inlet and a pressure side outlet, a condenser, a conduit connecting said compressor outlet to said condenser, means connecting said condenser to the inlets of each of said evaporator coils, and means connecting the outlets of said evaporator coils to said compressor inlet to complete a refrigerating cycle; valve means for controlling each of the said connecting means connected to the inlets and outlets of said evaporator coils; a hot gas header connected to said outlet of said compressor, means connecting said hot gas header to each of said evaporator coils, valve means for controlling said last mentioned means; means connecting each said evaporator coil to the said inlet of at least one other of said evaporator coils downstream of the said valve means for controlling said inlet of said other evaporator coils, valve means for controlling each of said last mentioned connecting means; said valve means for controlling the said connecting means from the condenser to the inlets of theV evaporator coils selectively operable for stopping refrigerant flow to` selected evaporator coils, said valve means for controlling the said connecting means from the evaporator coil outlets to the compressor inlet selectively opera'ole for stopping refrigerant flow from certain of those said selected evaporator coils to said compressor, said valve means for controlling the saidconnecting means from said hot gas header to the evaporator coils selectively operable for causing hot gaseous refrigerant to ow from the compressor to those said certain selected evaporator coils for defrosting those evaporator coils and condensing the refrigerant, and said valve means for controlling the said connecting means from said evaporator coil to the inlet of other evaporator coil-s selectively operable for causing the refrigerant used in defrosting those said certain selected evaporator coils to iioW to the inlets of the other said selected evaporator coils and be evaporated therein.

7. The refrigerating system of claim 6 having a clock means for selectively operating said valve means to positions for refrigerating and defrosting the said fixtures.

8. ln a refrigerating system employing a plurality of separate refrigerating fixtures each having evaporator coils, a compressor having a suction inlet and a pressure side outlet, a condenser-receiver means, a conduit connecting said compressor outlet to said condenser-receiver means, means connecting said condenser-receiver means to the inlets of each of said evaporator coils, and means connecting the outlets of said evaporator coils to said compressor inlet to complete a refrigerating cycle; valve means for controlling each of said connecting means connected to the inlets of said evaporator coils,`each of said Valve means having temperature responsive means positioned in the refrigerating fixture that has the evaporator coil associated with the connecting means controlled by that valve means for opening and closing that valve means and supplying liquid refrigerant to the associated evaporator coil for maintaining the predetermined temperature Within the associated refrigerating tixture, and valve means for controlling each of said connecting means connected to the outlets of said evaporator coils; a hot gas header connected to said outlet of said compressor, means connecting said hot gas header to the said evaporator coils, valve means for controlling said last-mentioned means; means connecting each said evaporator coil to the said inlet of at least one'other of said evaporator coils downstream of the said valve means for controlling said inlet of said other evaporator coils, valve means for controlling each of said last-mentioned connecting means; said valve means for controlling the said connecting means from the condenserreceiver means to the inlets of the evaporator coils selectively operable for stopping liquid refrigerant flow to selected evaporator coils and for deactivating the control by said temperature responsive means on those selectively operated valve means, said valve means for controlling the said connecting means from the evaporator coil outlets to the compressor inlet selectively operable for stopping refrigerant flow from certain of those said selected evaporator coils to said compressor, said valve means for controlling the said connecting means from said hot gas header to the evaporator coils selectively operable for causing hot gaseous refrigerant flow from the compressor to those said certain selected evaporator coils for defrosting those evaporator coils and condensing the refrigerant, and said valve means for controlling the said connecting means from said evaporator coil to the inlet of other evaporator coils selectively operable for causing the refrigerant used in defrosting those said certain selected evaporator coils to flow to the inlets of the other said selected evaporator coils and be evaporated therein.

9. Ina refrigeration system with a plurality of refrigerating fixtures and employing compressor means having a suction inlet and a high pressure outlet and a condenserreceiver means connected to the outlet for condensing the hot gaseous refrigerant to maintain a supply of liquid refrigerant, the combination of: a liquid header connected to the condenser-receiver means, a suction header connected to the suction inlet of the compressor means, a hot gas header connected to the high pressure outlet of the compressor means; a plurality of evaporator means having inlet and outlet sides connected in parallel between said liquid header and said suction header respectively and associated with the plurality of refrigerated fixtures for evaporating liquid refrigerant to cool the refrigerated fixtures and to provide a superabundant head load in the evaporated refrigerant returned to said suction header; means for selectively connecting one of said evaporator means to and between said hot gas header and the liquid header side of at least one other of said evaporator means of predetermined minimum capacity for conducting hot gaseous refrigerant from said not gas header through the one evaporator me ans for defrosting that one evaporator means and condensing the refrigerant, and for conducting that condensed refrigerant through the other of said evaporator means for reevaporating the refrigerant; a temperature responsive means associated with each refrigerated fixture, means for controlling the liquid refrigerant supply to each of said evaporator means from the liquid header controlled by each said temperature responsive means Vand for preventing normal liquidrefrigerant flow to said one evaporator means and said other evaporator means during derosting of said one evaporator means.

l0. The refrigeration system according to claim 9 in which said last-mentioned means comprises plural valve means, some of which are Vconfrolled by said temperature responsive means during normal refrigeration of said evaporator means, and at least one of which substantially restricts normal refrigerant ow to said one and other evaporator means during defrosting of said one evaporator means.

11. In a refrigerating system having a compressor with a suction side connected to a suction header and a discharge side connected to condenser-receiver means for providing a liquid refrigerant source, a liquid header connected to the condenser-receiver means, first refrigerating fixture means having irst evaporator means connected hetween said liquid and suction headers, a hat gas header connected to the discharge side of said compressor, tir-st valve means for selectively isolating said first evaporator means from said liquid and suction headers and connecting said iirst evaporator means to the hot gas header for receiving hot gaseous refrigerant from said compressor to eect the defrosting of said iirst evaporator means; the improvement comprising a multitude of other refrigerating fixtures having other evaporator means connected between said liquid and suction headers, at least several of said other evaporator means of said multitude of other refrigerating fixtures being connected for normal refrigeration during defrosting of said first evaporator means and forming a constant and superabundant source of latent heat to be returned to said compresse-r whereby said hot gaseous refrigerant in said hot gas header has a substantially greater heat load than required for defrosting said first evaporator means, and means for causing a reduced pressure on the inlet side of at least one of said other evaporator means relative to the pressure in said liquid header from said condenser-receiver means and for conducting liquid refrigerant resulting from the defrosting of said first evaporator means to the liquid header inlet side of said last-mentioned other evaporator means downstream of the said means for causing reduced pressure on such inlet side, said last-mentioned other evaporator means having a predetermined minimum refrigerant requirement suiiicient to vaporize the liquid refrigerant resulting from such defrost.

References Cited in the file of this patent UNITED STATES PATENTS 2,496,143 Backstrom Jan. 3l, 1950 2,667,757 Shoemaker Feb. 2, 1954 2,960,840 osken Nov. 22, 1960 2,978,877 Long Apr. 11, 1961 FOREIGN PATENTS 50,101 Germany Ian. 1l, 1890 

1. IN A REFRIGERATING SYSTEM HAVING A COMPRESSOR WITH A SUCTION SIDE CONNECTED TO A SUCTION HEADER AND A DISCHARGE SIDE CONNECTED TO CONDENSER-RECEIVER MEANS FOR PROVIDING A LIQUID REFRIGERANT SOURCE; A LIQUID HEADER, CONNECTED TO THE CONDENSER-RECEIVER MEANS, FIRST REFRIGERATING FIXTURE MEANS HAVING FIRST EVAPORATOR MEANS HAVING INLET AND OUTLET SIDES CONNECTED BETWEEN SAID LIQUID AND SUCTION HEADERS, A PLURALITY OF OTHER REFRIGERATING FIXTURES HAVING OTHER EVAPORATOR MEANS HAVING INLET AND OUTLET SIDES CONNECTED BETWEEN SAID LIQUID AND SUCTION HEADERS, A HOT GAS HEADER CONNECTED TO THE DISCHARGE SIDE OF SAID COMPRESSOR, FIRST VALVE MEANS FOR SELECTIVELY ISOLATING SAID FIRST EVAPORATOR MEANS FROM SAID SUCTION HEADER AND CONNECTING ONE SIDE OF SAID FIRST EVAPORATOR MEANS TO THE HOT GAS HEADER FOR RECEIVING HOT GASEOUS REFRIGERANT FROM SAID COMPRESSOR TO EFFECT THE DEFROSTING OF SAID FIRST EVAPORATOR MEANS, AT LEAST SEVERAL OF SAID OTHER EVAPORATOR MEANS BEING CONNECTED IN THE SYSTEM FOR NORMAL REFRIGERATION DURING DEFROSTING OF SAID FIRST EVAPORATOR MEANS AND RETURNING A SUPERABUNDANT LATENT HEAT LOAD TO SAID COMPRESSOR WHEREBY SAID HOT GASEOUS REFRIGERANT IN SAID HOT GAS HEADER HAS A SUBSTANTIALLY GREATER HEAT LOAD THAN REQUIRED FOR DEFROSTING SAID FIRST EVAPORATOR MEANS, AND MEANS FOR CAUSING A REDUCED PRESSURE ON THE INLET SIDE OF AT LEAST ONE OF SAID OTHER EVAPORATOR MEANS RELATIVE TO THE PRESSURE ON THE CONDENSER-RECEIVER MEANS AND FOR CONDUCTING THE 